What is the CHEAPEST per load laundry detergent without additives that is readily available?

My son uses All, which one of the cheapest per load and he loves it. I’m partial to tide, more expensive, but gets clothes cleaner.

My mom uses Borax stuff. But I don’t know what it’s made of.

Define “without additives.”

Soap flakes. It’s soap that’s been grated. It’s the original laundry detergent but fell out of favour for more fancy concentrated stuff with all the additives I’m assuming you don’t want. It’s making a come back now as a ‘natural’ alternative which has made it more expensive.

Straight lye soap. Cut the bars into cubes of usable size.

If you’re on a septic system, you might want to check the link below to see if the detergent you pick is good for it. Septic systems are obscenely expensive to clean, and I am taking great care to make mine last as long as possible between cleanings.

I use 7th generation, but I will also use Arm and Hammer free and clear.

https://www.bobvila.com/articles/best-laundry-detergents-for-septic-systems/

That would be Dr. Bronner’s Sal Suds.
Yes, it’s organic.
But per serving… it is cheaper than anything else, due to its concentration.
Because it is vegetable soap, however, you’ll need to put a little bit of vinegar in the rinse cycle to prevent residue buildup.